Multiwave range receiver



Jan. 311, 119 3% E. ZEPLER MULTIWAVE RANGE RECEIVER Filed NOV. 17, 1936 PR/OH A a T Q Rf v. 0% E T v N N R E 0 ma w 1 Patented Jan. 31, 1939 UNITED STATES 2,145,tit

PATENT oFFifcE MULTIWAVE RANGE RECEIVER many Application November 1'7, 1936, Serial No. 111,179 In Germany November 4, 1935 4 Claims.

In order to provide unicontrol tuning in radio receivers, it is known in the prior art to balance the input capacities of the oscillating circuits by special trimmers. For increasing the accuracy trimmers are not only connected to the tuning condensers but special trimmers are provided for the individual coils of the different wave ranges which are brought in circuit whenever the coordinated wave range is cut-in and which are the means to equalize the differences of the coil capacities in the individual wave ranges.

In the accompanying drawing Fig. 1 shows a circuit arrangement according to the prior art, and Fig. 2 discloses the improvement in such circuit arrangement according to the present invention.

Referring to Fig. l the tuning condenser is denoted by C and the coordinated trimmer by C. Special trimmers C1 and C2 are disposed in addition across coils L1 and L2, these latter being switched in by switches S1 and S2 according to the wave range through which it is desired to tune.

In the case of a capacitative coupling of the antenna through a condenser CA, trimmer C in the input circuit is omitted but used in the subsequent circuits, for capacity CA is actually connected in parallel with the oscillation circuit through the antenna-earth capacity. Now, it would be desirable to omit also the trimmers C1 and C2 since in that case the coupling capacity CA could be correspondingly increased. This is not feasible however, as the self-capacity of coils L1 and L2 can be smaller than that of the coils in the subsequent circuits so that the trimmers still have to be utilized.

According to the invention, in multi-circuit receivers with special trimmers connected to the coils of difierent wave range, the coil trimmers of the input circuit each have one side connected to the grid end of its associated coil, and its other side connected through the wave range switch to the antenna instead of to the grounded end of the coil or input circuit.

Fig. 2 shows an exemplified embodiment of the invention. It may be seen that the lower connections of trimmers C1 and C2 are connected to the contacts of switch S3 and that with the switching in of diiferent wave ranges the corresponding trimmer is connected in parallel with coupling condenser CA. The coupling of the antenna is therefore made closer Without increasing the initial capacity of the circuits. In fact, the initial capacities of the input circuits must not be increased at will otherwise the wave ranges would be considerably restricted with a given minimum capacity of the rotary condensers.

For greater clarity, it is to be noted that the invention refers expressly to multi-stage receivers and to a capacitive antenna coupling in such receivers. The purpose of the invention consists in increasing the antenna coupling and thereby the volume without the necessity of increasing the incipient capacitances of the tuning circuits. To be sure, the antenna coupling condenser CA has to be considered as incipient capacitance of the first tuned circuit. The solution consists, as compared to the known arrangement according to Fig. l, in not coupling the coil trimmers C1, C2 tightly to the single coils: of the various Wave ranges but in connecting said trimmers according to Fig. 2 in parallel to the coupling condenser CA. The condenser CA is, of course, unnecessary if the capacitances C1 and C2 are chosen correspondingly large. This possibility has heretofore been mentioned. However, in the arrangement according to the invention (Fig. 2), the condenser CA is provided for the sole reason that then the variable capacitances C1 and C2 need not be too large. They are only intended for balancing the small difference of the coil capacitances.

The invention is not limited to the type of coil switching circuit as illustrated but may be applied to rotary coil systems or switching operations by short-circuiting a part of the coils or to plug coils whereon the coil trimmers are disposed. In the latter case the plugs and plug sockets may be considered as a wave switch.

Having described my invention, what I claim as novel and desire to secure by Letters Patent is:

1. In a radio receiver, the combination of a vacuum tube having a cathode, grid and plate, an adjustable tuning condenser connected between said grid and cathode, a coil shunted across said tuning coil to the opposite sides of said condenser, an antenna, a circuit including a coupling capacity connecting said grid and said antenna, and a condenser having one side connected to the grid end of said tuning condenser and its other side to said antenna, whereby said last mentioned condenser is effectively in shunt to said antenna coupling capacity.

2. In a radio receiver, the combination of a vacuum tube amplifier having a cathode, grid and anode, an adjustable tuning condenser connected between said grid and cathode, a coil having its terminals connected between the opposite sides of said condenser, an antenna, a fixed condenser connected to said antenna and grid, and

a variable condenser connected in shunt with said fixed condenser, said fixed condenser, variable condenser and the capacity of said antenna together constituting a trimmer capacity adapted to adjust the tuning of the circuit comprising said coil and adjustable tuning condenser to a predetermined frequency.

3. In a radio receiver, the combination of a vacuum tube amplifier having a cathode, grid and anode, an adjustable tuning condenser connected between said grid and cathode, a plurality of coils having difierent inductance values, means for selectively connecting the terminals of anyone of said coils between the opposite sides of said tuning condenser, an antenna, a plurality of adjustable condensers, one for each of the coils, and a switching device arranged to selectively connect an appropriate one of said last named condensers depending upon the selector coil, in series between said antenna and said grid.

4. In a radio receiver, the combination of a vacuum tube having a cathode, grid and plate, an adjustable tuning condenser connected between said grid and cathode, a plurality of coils having difierent inductance values, a switching device for selectively connecting the terminals of anyone of said coils between the opposite sides of said tuning condenser, an antenna, a coupling condenser connected between said antenna and grid, a plurality of adjustable trimmer condensers, one for each of the coils, a connection from one side of each trimmer condenser to the high potential end of the corresponding coil, and a second switching device for selectively connecting the other side of the selected trimmer condenser to the antenna, said switching devices being controlled to operate in unison.

ERICH ZEPLER. 

